When Wal-Mart Stores does a thing, it does it big. The stock buy-back it announced at its annual meeting today is no exception, at $15 billion, hot on the heels of an earlier $15-billion repurchase plan.

So it’s probably a good time to remember that stock buybacks generally aren’t the unparalleled good that they can seem at first glance.

It has been a big week so far for the market cops at the Securities & Exchange Commission: Each day brought a new multimillion-dollar settlement, most involving high-profile people or companies—Bank of America (BAC), General Electric (GE), and two former executives of American International Group (AIG), plus two smaller trading firms.

President Barack Obama's plan to overhaul financial regulation covers everything from mortgages to hedge funds. But reform efforts in Europe may prove more significant for U.S. companies. European regulators are hashing out new rules for banks, insurers, and money managers that could put U.S. firms at a disadvantage.

World leaders are talking bravely about fixing the global financial system. As the Group of Twenty heads toward an important summit in Pittsburgh on Sept. 24-25, they are vowing to bang out a regulatory structure that will keep rich, careless bankers from once again driving their firms to ruin and then getting bailed out by taxpayers.